As shown in FIG. 1, an exercise wheel of the prior art comprises a hollow shaft 11 which is provided at one end thereof with a long slot 12 of a length and extending toward the midsection thereof, a volute spring 13 provided in the center thereof with a locating piece 131 which is retained in the long slot 12, and two rollers 14 which are provided at the center thereof with a round hole 15. Both ends of the shaft 11 are fitted into the round holes 15 of the two rollers 14. The two rollers 14 are joined together in the middle of the shaft 11 such that the volute spring 13 is confined in the rollers 14. The two rollers 14 are provided in the peripheral edges of the round holes 15 thereof with a hollow guide pillar 16 for fastening a bolt 17. One of the two hollow pillar 16 is shorter than other so as to enable the bolt 17 to be exposed to facilitate the connecting of the locating piece 132 of the outer end of the volute spring 13. In operation, the user of the exercise wheel stoops in such a manner that his or her hands hold both ends of the shaft 11 to push the rollers forward on a surface. As the rollers are pushed to roll, the volute spring 13 is compressed to store the elastic recovery force.
Such a prior art exercise wheel as described above is defective in design in that the rollers can not be rolled stably on the surface by both hands holding both ends of the hollow shaft in light of the center of gravity tending to deflect. In addition, the elastic recovery force provided by the volute spring is inadequate.